Saving log data using a disk system as primary cache and a tape library as secondary cache

ABSTRACT

Various embodiments are provided for saving a log data in a hierarchical storage management system using a disk system as a primary cache with a tape library as a secondary cache. The user data is stored in the primary cache and written into the secondary cache at a subsequent period of time. Blank tapes in the secondary cache are prepared for storing the user data and the log data, based on priorities. At least one of the blank tapes is selected for copying the log data and the user data from the primary cache to the secondary cache based on priorities. The log data is stored in the primary cache.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/029,435, filed on Sep. 17, 2013, which is a Continuation of U.S.patent application Ser. No. 12/966,046, filed on Dec. 13, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to computers, and moreparticularly to method embodiments for saving log data in a hierarchicalstorage management (HSM) system using a disk system as a primary cachewith a tape library as a secondary cache in a computing storageenvironment.

2. Description of the Related Art

Log data generated from microcodes of a hierarchical storage management(HSM) system, typified by a virtual tape server (VTS) or the like, isstored in a hard disk which is the system's primary cache. The primarycache, however, is generally limited in storage area in comparison withthe secondary cache. Therefore, the amount of log data which can be leftis limited, and usually the old log data is overwritten as new log datais logged or written into storage. In addition, such log data is lessimportant than user data, or other data, and therefore it is difficultto secure a large size for the primary cache as a storage area forlogging. However, if a problem occurs at a customer's office, theproblem analysis is performed on the basis of the logged data that isstored and any extremely old log data may be necessary for properanalysis to solve the particular problem. Older logged data, however,often times is lost after overwriting (wrapping) with newer logged data,making it difficult to perform the problem analysis.

SUMMARY OF THE INVENTION

In view of the current state of the art, a need exists for saving logdata in a hierarchical storage management (HSM) system using a disksystem as a primary cache with a tape library as a secondary cache in acomputing storage environment. In a hierarchical storage environment,for example, a virtual tape server (VTS) uses a disk system as theprimary cache with a tape library as the secondary cache on the back endfor storage on real or virtual tape cartridges (tape). User data isstored first in the disk system and then moved to a tape cartridge at anappropriate timing. In this operation, a sufficient number of blanktapes are prepared in the tape library and are unused until user data isactually written into the tapes. In wrapping of the microcode log storedin the primary cache, the VTS microcode log is copied into the blanktape. Since the tape in which the log is written still looks like ablank tape to the user, the tape is likely to be used eventually. Thus,the log data is reserved for a longer period of time by causing the tapecontaining the written or stored logged data to be selected at thelatest possible time for writing user data. In addition, the blank tapesare not limited to a microcode debug log, but various histories of theentire VTS such as a system load status and event information can beleft as much as possible. Thus, log data having many histories can beleft in comparison with a case where log data is stored only in the disksystem. Moreover, this does not cause any load on the user and log datais preserved as long as possible.

Accordingly, in view of the foregoing and to achieve the benefits in theprevious summary, various embodiments are provided for saving log datain a hierarchical storage management (HSM) system using a disk system asa primary cache with a tape library as a secondary cache in a computingstorage environment. In one embodiment, by way of example only, the userdata is stored in the primary cache, the user data being written fromthe primary cache into the secondary cache at a subsequent period oftime. Blank tapes are prepared in the secondary cache for storing theuser data and the log data based on priorities, the blank tapes areunused until the user data is written to the tape library. A blank tapeis selected for copying the log data and the user data from the primarycache to the secondary cache based upon priorities. The log data isstored in the primary cache, wherein the plurality of log data iswrapped in the primary cache and a copy of the plurality of microcodelog data being copied into the plurality of blank tapes, the pluralityof blank tapes being configured to appear blank to a user for storingthe user data.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict embodiments of the invention and are not therefore to beconsidered to be limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings, in which:

FIG. 1 illustrates an exemplary embodiment of a representative virtualtape system;

FIG. 2 illustrates an exemplary embodiment of the VTS and librarymanager;

FIG. 3A illustrates exemplary embodiment for logging data from the VTSto the tape library;

FIG. 3B illustrates an exemplary embodiment for logging data from theVTS to tape cartridges;

FIG. 4 illustrates an exemplary functionality of the threshold value formigrating log data;

FIG. 5 illustrates an exemplary method for moving log data from theprimary cache to the secondary cache; and

FIG. 6 illustrates exemplary method for moving user data from theprimary cache to the secondary cache.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary embodiment of a representative virtualtape system 100, in accordance with the present invention. The system100 includes a tape library 102, at least one VTS 104 (primary cache),and at least one host 106 (shown as 106 a and 106 b). Each host 106 maybe a mainframe computer. Alternatively, the host (users) 106 may beservers or personal computers using a variety of operating systems. Thehost 106 and the VTS 104 are connected via a storage area network (SAN)108 or another suitable communications channel, for example, anEnterprise System Connection (ESCON) channel used in IBM mainframecomputers.

The tape library 102 may include a library manager 110, one or more datadrive devices, which may be tape cartridges 112 (secondary cache shownas 112 a-e), an accessor 114, and a plurality of mountable media 116. Inone embodiment, the mountable media 116 includes tape cartridges,magnetic disks, optical disks, CDs, DVDs, other devices that can storedata and be mounted to a drive unit, and the like. The library manager110, which includes at least one computing processor, may beinterconnected with and may control the actions of the tape cartridges112 and the accessor 114. The configuration of the library manager 110will be shown and described in greater detail below. The mechanisms ofthe illustrated embodiments use two types of cache, a primary cache (VTS104) and a secondary cache (tape cartridges, 350 in FIG. 3) in thehierarchical storage management (HSM) system. Such configuration allowsthe VTS 104 to present to the user or host 106 a file on the disk cache(308, in FIG. 3) as if it were a virtual tape and the user writes orreads data to or from the file. The file, as the virtual tape generatedby the host, is later migrated to a real tape (tape cartridges, 350 inFIG. 3) at an appropriate time. However, the mechanisms of theillustrated embodiments may provide for the real tape or tape cartridges(350 in FIG. 3) to be real or virtual.

In FIG. 1, five tape cartridges 112 a, 112 b, 112 c, 112 d, and 112 eare shown. The present invention is operable with one or more tapedrives 113. The tape drives 113 are configured for assisting with themounting and demounting user data and log data. The tape cartridges 112may share one single repository of mountable media 116. Alternatively,the tape cartridges 112 may utilize multiple repositories of mountablemedia 116. The tape cartridges 112 may advantageously be distributedover multiple locations to decrease the probability that multiple tapecartridges 112 will be incapacitated by a disaster in one location.

The interconnections between the library manager 110, the tapecartridges 112, and the accessor 114 are shown as dashed lines toindicate that the library manager 110 transmits and receives controlsignals, rather than data to be stored or retrieved, to the tapecartridges 112 and/or the accessor 114. Data for storage or retrievalmay instead be transmitted directly between the VTS 104 and the tapecartridges 112 via a network 118, which may be a storage area network,(SAN), local area network (LAN), wide area network (WAN), or anothersuitable type of network, including the Internet or a direct connectionbetween the VTS 104 and the tape cartridges 112 via a point to point ormulti-drop buss connection, for example, a Small Computer StorageInterface (SCSI) interface. Alternatively, control signals for tapedrives 112 can be transmitted and received through connections betweenthe VTS 104 and the library manager 110 and the VTS 104 and the tapedrives 112 via network 118.

The accessor 114 may be a robotic arm or another mechanical deviceconfigured to transport a selected mountable media 116 between a storagebin and tape cartridges 112. The accessor 114 typically includes agripper and a bar code scanner, or a similar read system, mounted on thegripper. The bar code scanner is used to read a volume serial number(VOLSER) printed on a cartridge label affixed to the tape cartridge 112.In alternative embodiments, the tape cartridges 112 may be replaced byoptical disk drives or other magnetic drives. Similarly, the mountablemedia 116 and the tape drive 113 may include magnetic media, opticalmedia, or any other removable media corresponding to the type of driveemployed. A control console 120 may be connected to the library manager110. The control console 120 may be a computer in communication with thelibrary manager 110 so that a user can control the operating parametersof the tape library 102 independently of the host 106.

In addition, the described exemplary embodiment may be implemented byvarious means, such as hardware, software, firmware, or a combinationthereof operational on or otherwise associated with the computingenvironment. For example, the method 100, as well as the followingillustrated exemplary methods may be implemented, partially or wholly,as a computer program product including a computer-readable storagemedium having computer-readable program code portions stored therein.The computer-readable storage medium may include disk drives, flashmemory, digital versatile disks (DVDs), compact disks (CDs), and othertypes of storage mediums as has been previously described.

FIG. 2 illustrates a schematic block diagram depicting one embodiment ofthe VTS 104 and one embodiment of the library manager 110 of FIG. 1. TheVTS 104 and the library manager 110 may each take the form of a computerwith a bus, processor, memory, and the like. These elements have beenomitted from FIG. 2 to more clearly depict the various executablemodules and data blocks of the VTS 104 and the library manager 110pertinent to the invention. There could also be other executable modulesand data blocks known in the art in implementing a VTS 104 or librarymanager 110, but are omitted to focus on the elements essential to theinvention.

As shown, the VTS 104 includes a plurality of virtual tape drives 200, afile system manager 202, an automated storage manager 206, a queue 208,and at least one direct access storage device (DASD) cache 210. The DASDcache 210 temporarily stores data from the host 106 on virtual orlogical volumes in the form of files, and may thus be referred to as aprimary cache. A write command from the host 106 is processed by the VTS104, through a virtual tape drive 200 into the DASD cache 210, prior totransferring the updated logical volume from the DASD cache 210 to themountable media or physical volume 116 (FIG. 1). According to oneexample, the DASD cache 210 takes the form of one or more hard diskdrives, which may be arranged in a redundant array of independent drives(RAID configuration), such as RAID 5. The virtual tape drives 200 alsoprocess control commands from host 106.

The file system manager 202 manages and coordinates data storage in theDASD cache 210. The automated storage manager 206 controls the interfacecommunications between the file system manager 202 and the tapecartridges 112. The automated storage manager 206 also controlscommunications between the VTS 104 and the library manager 110. In oneembodiment, the host 106 may request a particular logical volume. Theautomated storage manager 206 determines whether the logical volume isin the DASD cache 210. If it is not, the automated storage manager 206requests a recall for it from the physical volume or mountable media116. The automated storage manage 206 may also contain a queue 208 fortemporarily placing additional recall requests to be processed. Thus,the automated storage manager 206 is an apparatus for recalling logicalvolumes from mountable media 116 by means of the tape drives 112 a, b,c, d, and e (FIG. 1).

The library manager 110 manages the virtual and physical volumes as wellas the constructs. More specifically, the library manager 110 includesthe command processor 225 that receives control commands from thevirtual tape drives 200 and the automated storage manager 206. Thecommand processor 225 passes instructions about the management of thevirtual and physical volumes to the volume manager 235. The volumemanager 235 stores information about the virtual and physical volumes ona database 230 of the library manager 110. In addition, depending on theinstructions received, the volume manager sends instructions to the tapecartridges 112 and/or the accessor 114 to load or “mount” the cartridgesor other mountable media 116 on which copies of the virtual volume areto be made or retrieved. Mounting of multiple cartridges 116 may begenerally simultaneous or in a certain order, depending on theconfiguration of the accessor 114 and the tape cartridges 112.

The library manager 110 also has a construct manager 240 that receivesuser instructions from the control console 120 regarding the volumemanagement actions to be followed for a given construct name. The volumemanagement actions are stored and retrieved by the construct manager 240on a database 230 of the library manager 110. For certain controlcommands received by the command processor 225, the command processor225 instructs the construct manager 240 to provide the volume managementactions for a specific virtual volume. The command processor 225 thenpasses the returned volume management actions for a specific virtualvolume to the automated storage manager 206.

Turning now to FIG. 3A, an exemplary embodiment 370 of the VTS 104 andone embodiment of the tape library for logging data from the VTS to tapelibrary 102 of FIG. 1. The present invention includes the use of twotypes of cache in the hierarchical storage management (HSM) 306 systems.There could also be other executable modules and data blocks known inthe art in implementing a VTS 104 or tape library 110, but are omittedto focus on the elements essential to the invention. In one embodiment,the exemplary embodiment 370 may be implemented using variousprocessing, networking, and storage components in computingenvironments.

The VTS 104 presents to the host (user) 106 a file on the disk cache 308as if it were a virtual tape and the host 106 writes or reads data to orfrom the file. The file as the virtual tape generated by the host 106 islater migrated to the tape drives 113 or tape cartridges 350 of tapelibrary 102 at an appropriate time. (The mechanisms of the illustratedembodiments provided in FIG. 3 are further explained in FIG. 3B) Thepresent invention is operable with one or more tape drives 113. The tapedrives 113 are configured for assisting with the mounting and demountinguser data and log data to and from the tape cartridges (tape media) 112.

Turning now to FIG. 3B, an exemplary embodiment 375 of the VTS 104 andone embodiment of the tape library for logging data from the VTS 104(FIG. 1) to tape cartridges 350. As mentioned in FIG. 3A, the presentinvention includes the use of two types of cache in the hierarchicalstorage management (HSM) 306 system. There could also be otherexecutable modules and data blocks known in the art in implementing aVTS 104 or tape library 102, but are omitted to focus on the elementsessential to the invention. In one embodiment, the exemplary embodiment375 may be implemented using various processing, networking, and storagecomponents in computing environments.

The mechanisms of the illustrated embodiments are such that during thesystem operation, the tape cartridges 350 (real or virtual tapes) of thetape library 102 will normally transits three types of states. The threetypes of states include: blank tapes 112 a in which no data is written,halfway written tapes 112 b in which data is written halfway of the tapelibrary, and completely written tapes 112 c in which data is written upto the end of the tape cartridge in the tape library. When the user datafile on the disk cache 308 is migrated to the tape cartridges 350 of thetape library 102, the destination tape cartridge 112 is selected by thefollowing priorities: halfway written tapes 112 b and blank tapes 112 a.As will be explained later, the tape cartridge is blank tape with logdata written halfway 112 d and 112 e is a blank tape with completelywritten and filled with log data. A host 106 generally prepares asufficient number of blank tapes 112 a and replenishes new tapes or tapecartridges 350 in the tape library 102 in case of running out of blanktapes 112 a. Therefore, the host 106 hardly uses up all of the blanktapes 112 a. In the present invention, the blank tapes 112 a are used tostore old microcode log and log data indicating system load statuses.Generally speaking, while a blank tape in which a log file is writtenmay look like a normal blank tape 112 a to the user, the tape is furtherclassified into the following three types in the system: a blank tapewith no log data 112 a where no data is written, blank tape with logdata written halfway 112 d in which log data is written halfway, and ablank tape with log data written completely 112 e, which is completelyfilled with log data. The present invention is operable with one or moretape drives 113. The tape drives 113 are configured for assisting withthe mounting and demounting user data and log data to and from the tapecartridges 112.

In one aspect of the illustrated embodiments, log data is moved from thedisk cache 308 (primary cache) to the tape library 102 (secondary cache)in a procedural order. First, the size of log data or the like on thedisk cache 308 exceeds a certain threshold. Second, one of the tapecartridges 350, containing the various types of blank cartridges 112, isselected by the priorities described below. Third, the log data iswritten into the tape cartridges 350 selected in step. Finally, theprocessing returns to the first step, as previously mentioned.

The threshold in the above first step is assumed to be determined asdescribed below in FIG. 4. The timing at which the log data is moved tothe tape library 102 is when the log data on the disk cache 308 reachesa certain threshold amount. Although the log data area on the disk cache308 is used with wrapping, as is conventional, a threshold value isdetermined so that data can be moved before the data is overwritten bywrapping. In addition, one tape drive 113 is used to write log data intoone of the tape cartridges 350, and thus, one tape drive 113 used forthe user data migration is temporarily occupied. Therefore, it isnecessary to reduce as low as possible the frequency of writing the logdata into the tape library 102.

Turning now to FIG. 4, exemplary functionality 400 of the threshold formigrating log data, as previously described is illustrated. Theexemplary functionality 400 includes 5 blocks; block 420, block 430,block 440, block 460, and block 480. Within each block are valuesillustrating the functionality of the threshold for determining when towrite the log data. S_log spc 410 is the size of the log data area inwhich log data can be written on the disk cache. S_threshold 404 is thethreshold value used to determine when to write data, as previouslydescribed in FIG. 3, S_buf 408 is a spare area prepared for anunexpected occurrence. S_residual 406 is the amount of log data that canbe written into the log data area after log data reaches the threshold,and V_sys log 402 is the amount of log data output per unit time fromthe system. The write area 425 is the area in which the log data iswritten. T_mnt 411 is the time required for moving the tape cartridge112 to the tape drive 113 (FIG. 3A), mounting the tape, and locating thestart of the log data on the tape cartridge 112, the amount of logoutput from the system during the time T_mnt is V_sys log*T_mnt 412.

In one of the illustrated embodiments, blocks 420 and 430 illustrate thewrite area 425 where the log data is written. S_log spc 410 is the sizeof the log data area in which log data can be written on the disk cache.S_threshold 404 is the threshold as previously described in FIG. 3,S_buf 408 is a spare area prepared for an unexpected occurrence.S_residual 406 is the amount of log data that can be written into thelog data area after log data reaches the threshold and V_sys log 402 isthe amount of log data output per unit time from the system. The writearea 425 is the area in which the log data is written. The log data ofthe S_threshold 404 amount is written into the tape cartridge 112 whenthe log reaches S_threshold 404 as illustrated by the dotted line insideof the block 420.

In reference to block 420, the S_threshold 404 has not yet reached theS_threshold 404 limit as represented by the dotted line in the writearea 425. The write area 425 is the area in which the log data iswritten. As the write area 425 reaches the S_threshold 404 limit, asillustrated in block 430, the amount of log data in the write area 425starts to be written into the tape library (102 of FIG. 1). Themechanisms of the illustrated embodiments continue to output the logdata while the log data of the S_threshold 404 amount is written into onof the tape library (102 of FIG. 1), as seen in block 440. The S_log spc410 is the size of the log data area in which log data can be written onthe disk cache. S_threshold 404 is the threshold, as previouslydescribed in FIG. 3. S_buf 408 is a spare area prepared for anunexpected occurrence. S_residual 406 is the amount of log data that canbe written into the log data area after log data reaches the thresholdand V_sys log 402 is the amount of log data output per unit time fromthe system. A time period is represented by T_mnt 411 and is the timeperiod required for moving the virtual tape 104 to the tape library (102of FIG. 1), tape drives (113 of FIG. 3), mounting the tape, and locatingthe start of the log data on the tape. Moreover, the amount of log dataoutput occurring during the time T_mnt is represented by the equationV_sys log*T_mnt 412.

In reference to Block 460, when the log data of the S_threshold 404amount commences to write the log data into the tape library (102 ofFIG. 1), a written portion 466 is represented as a portion of the logdata that has been written into the tape library (102, FIG. 1). Thewriting speed at which the log data is written to the tape library (102,FIG. 1) is shown by V_tapewrt 414.

The exemplary functionality 400 as described previously, is demonstratedthrough a series of equations. Ideally, when the log of the S_threshold404 amount is completely written to the tape library (102, FIG. 1), theamount of new log output from the system or host (106, FIG. 1) is equalto the S_residual 406 amount. Therefore, the S_threshold value isobtained so as to achieve the S_residual 406 amount. The total time(T_log mig) required to write the log of the S_threshold 404 amount intothe tape library (102, FIG. 1) is shown by:

T_log mig=T _(—) mnt+S_threshold/V_tapewrt  (1),

where T_mnt 411 is the time required for moving the tape cartridge 112to the tape drive 113, mounting the tape, locating the start of the logdata on the tape cartridge 112, the S_threshold is the threshold value,and V_tapewrt writing speed at which the log data is written to the tapelibrary.

The amount of log output from the system or host (106, FIG. 1) duringthis time is required to be equal to the S_residual 406 value, and isdefined by:

S_residual=V _(—) sys log*T_log mig=V _(—) sys log*(T _(—)mnt+S_threshold/V_tapewrt)  (2)

where S_residual 406 is the amount of log data that can be written intothe log data area after log data reaches the threshold, V_sys log 402 isthe amount of log data output per unit time from the system, T_log migis the total time required to write the log of the S_threshold 404amount into the tape library, V_sys log 402 is the amount of log dataoutput per unit time from the system, T_mnt 411 is the time required formoving the tape cartridge 112 to the tape drive 113, mounting the tape,and locating the start of the log data on the tape cartridge 112,S_threshold is the threshold value, and V_tapewrt writing speed at whichthe log data is written to the tape library.

The following equation is satisfied when defined and shown as:

S_residual=S_log spc−S _(—) buf−S_threshold  (3)

where S_residual 406 is the amount of log data that can be written intothe log data area after log data reaches the threshold, S_log spc 410 isthe size of the log data area in which log data can be written on thedisk cache, the S_buf 408 value is a spare area prepared for anunexpected occurrence, S_threshold is the threshold value, and V_tapewrtwriting speed at which the log data is written to the tape library.

Because of equation (2) and (3), the following equations holds true asdefined and shown by:

S_log spc−S _(—) buf−S_threshold=V _(—) sys log*(T _(—)mnt+S_threshold/V_tapewrt)  (4)

where S_log spc 410 is the size of the log data area in which log datacan be written on the disk cache, the S_buf 408 value is a spare areaprepared for an unexpected occurrence, S_threshold is the thresholdvalue, V_sys log 402 is the amount of log data output per unit time fromthe system, T_mnt 411 is the time required for moving the tape cartridge112 to the tape drive 113, mounting the tape, locating the start of thelog data on the tape cartridge 112, and V_tapewrt writing speed at whichthe log data is written to the tape library.

If the S_threshold 404 value is calculated based on the above equation,the threshold value is determined by solving the following equation toobtain the equation defined and shown by:

S_threshold=(S_log spc−S _(—) buf−T _(—) mnt*V _(—) sys log)/(1+V _(—)sys log/V_tapewrt)  (5)

where S_threshold is the threshold value, S_log spc 410 is the size ofthe log data area in which log data can be written on the disk cache,the S_buf 408 value is a spare area prepared for an unexpectedoccurrence, V_sys log 402 is the amount of log data output per unit timefrom the system, T_mnt 411 is the time required for moving the tapecartridge 112 to the tape drive 113, mounting the tape, locating thestart of the log data on the tape cartridge 112, and V_tapewrt writingspeed at which the log data is written to the tape library.

Generally, V_sys log 402 is sufficiently lower than V_tapewrt 414, andtherefore, if the following equation shown by:

V _(—) sys log/V_tapewrt≈0  (6)

where V_sys log 402 is the amount of log data output per unit time fromthe system and V_tapewrt writing speed at which the log data is writtento the tape library, than the following is satisfied shown and definedby:

S_threshold−S_log spc−S _(—) buf−T _(—) mnt*V _(—) sys log  (7)

Where S_threshold is the threshold value, S_log spc 410 is the size ofthe log data area in which log data can be written on the disk cache,the S_buf 408 value is a spare area prepared for an unexpectedoccurrence, V_sys log 402 is the amount of log data output per unit timefrom the system, and T_mnt 411 is the time required for moving the tapecartridge 112 to the tape drive 113, mounting the tape, and locating thestart of the log data on the tape cartridge 112.

Therefore, as illustrated in block 480, the equation S_threshold≈S_logspc−S_buf−T_mnt*V_sys log (7) is an approximation where writing the datato the tape library (102, FIG. 1) corresponds to moving the tapecartridge 112, mounting the tape cartridge 112, and locating the startof the log data on the tape cartridge 112. Also, the equation fordetermining the S_threshold 404, S_log spc 410, S_buf 408, V_tapewrt414, and T_mnt 411 can be derived from a specification, though V_sys log402 is likely to vary according to the system operating condition. Ifthe actual log data output speed is continuously measured and V_realsyslog, which is the measured value as a time function, the following V_syslog determination method may be obtained. The V_realsys log obtainedimmediately before the log data reaches the S_threshold 404 value isassumed to be V_sys log 402. In the VTS (104, FIG. 1), a variety ofactions may be performed in a one-day cycle. For example, the user datamay be stored in the daytime while the backend maintenance process maybe mainly performed during the nighttime. Therefore, V_realsys log maybe stored for each hour in a day and V_realsys log may be stored at thetime when the log data reaches the S_threshold 404 value that is assumedto be V_sys log.

FIG. 5, following, illustrates an exemplary method 500 for moving logdata from the primary cache to the secondary cache with the foregoingdiscussion in mind. Method 500 begins (step 502), by selecting theappropriate tape cartridge for writing the log data (step 504). If anyblank tapes with log data written halfway are present (step 506) themethod 500 will select the blank tape with log data written halfway andwrite the additional log data (step 514). If no blank tapes with logdata written halfway are found (step 506) the method 500 will check tosee if any blank tape with no log data are present (step 508). If ablank tape with no log data is found, the method 500 will select theblank tape with no log data and write the log data (step 512). However,if no blank tape with no log data exists, the method 500 will select theoldest blank tape with log data written completely and overwrite thetape cartridge (step 510). The method ends (step 516).

FIG. 6, following, illustrates an exemplary method 600 for moving a filewith user data from the primary cache to the secondary cache with theforegoing discussion in mind. Method 600 begins (step 602), by selectingthe appropriate tape cartridge for writing the user data (step 604). Ifany blank tapes with user data written half way are present (step 606)the method 600 will select the blank tape with user data written halfwayand write the additional user data (step 624). If no blank tapes withuser data written halfway are present (step 606) the method 600 willcheck to see if any blank tape with no log data is present (step 608).If a blank tape with no log data is found, the method 600 will selectthe blank tape with no log data and write the user data (step 620).However, if no blank tape with no log data exists, the method 600 willdetermine if any blank tape with log data written completely exists(step 610). If so, the method 600 will select the oldest blank tape withlog data written completely filled and overwrite the tape cartridge(step 616). If no blank tape with no log data exists, the method 600will select a blank tape with log data written halfway and overwrite thetape cartridge (step 612). The method ends (step 625). Thus, the logdata having many histories can be left blank tapes as compared withsituations where log data is stored only in the disk system (primarycache) and thus reducing the load on the host/user.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wired, optical fiber cable, RF, etc., or any suitable combination of theforegoing. Computer program code for carrying out operations for aspectsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer, other programmable data processing apparatus, orother devices to cause a series of operational steps to be performed onthe computer, other programmable apparatus or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the above figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

While one or more embodiments of the present invention have beenillustrated in detail, the skilled artisan will appreciate thatmodifications and adaptations to those embodiments may be made withoutdeparting from the scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. A method for saving a plurality of log data in ahierarchical storage management (HSM) system using a disk system as aprimary cache with a tape library as a secondary cache by a processordevice, comprising: storing user data in the primary cache, the userdata written from the primary cache into the secondary cache at asubsequent period of time; preparing a plurality of blank tapes in thesecondary cache for storing the user data and the plurality of log databased on a plurality of priorities, the plurality of blank tapes unuseduntil the user data is written to at least one tape media; selecting atleast one of the plurality of blank tapes for copying the plurality oflog data and the user data from the primary cache to the secondary cachebased upon the plurality of priorities; and storing the plurality of logdata in the primary cache, wherein the plurality of log data is wrappedin the primary cache and a copy of the plurality of log data copied intothe plurality of blank tapes, the plurality of blank tapes beingconfigured to appear empty to a user for storing the user data.
 2. Themethod of claim 1, further including delaying the selection of at leastone of the plurality of blank tapes, completely filled with theplurality of log data, for writing additional amounts of the user data,wherein the plurality of log data in at least one of the plurality ofblank tapes completely filled with the plurality of log data ispreserved for an extended period.
 2. The method of claim 1, furtherincluding determining a threshold value to allow the plurality of logdata to be copied from the primary cache to the secondary cache prior towrapping the plurality of log data.
 3. The method of claim 1, furtherincluding, copying the plurality of log data from the primary cache tothe secondary cache when a size of the plurality of log data on theprimary cache exceeds a threshold value.
 4. The method of claim 1,wherein selecting at least one of the plurality of blank tapes forcopying the plurality of log data from the primary cache to thesecondary cache based upon the plurality of priorities includesperforming at least one of: if the secondary cache contains at least oneof the plurality of blank tapes partially filled with the plurality oflog data, selecting the at least one of the plurality of blank tapespartially filled with the plurality of log data, if the secondary cachecontains at least one of the plurality of blank tapes without theplurality of log data, selecting the at least one of the plurality ofblank tapes without the plurality of log data, and if the secondarycache contains at least one of the plurality of blank tapes completelyfilled with the plurality of log data, selecting an oldest one of the atleast one of the plurality of blank tapes completely filled with theplurality of log data and overwriting the plurality of log data.
 5. Themethod of claim 1, wherein selecting at least one of the plurality ofblank tapes for copying the user data from the primary cache to thesecondary cache based upon the plurality of priorities includesperforming at least one of: if the secondary cache contains at least oneof the plurality of blank tapes partially filled with the user data,selecting the at least one of the plurality of blank tapes partiallyfilled with the plurality of log data, if the secondary cache containsat least one of the plurality of blank tapes without the plurality oflog data, selecting the at least one of the plurality of blank tapeswithout the plurality of log data, if the secondary cache contains atleast one of the plurality of blank tapes completely filled with theplurality of log data, selecting an oldest one of the at least one ofthe plurality of blank tapes completely filled with the plurality of logdata and overwriting the plurality of log data with the user data, andif the secondary cache contains at least one blank tape without theplurality of log data, selecting the oldest one of the at least one ofthe plurality of blank tapes partially filled with the plurality of logdata and overwriting the plurality of log data.
 6. The method of claim1, further including preparing the plurality of blank tapes in thesecondary cache for storing the user data and the plurality of log databy the plurality of priorities including performing at least one of:replenishing the secondary cache with an additional amount of theplurality of blank tapes, and for each of the plurality of priorities,adapting the plurality of blank tapes to operate in a plurality ofstates.